It is generally agreed that adequate respiratory control is necessary for successful speech production (45), and that respiratory control is somehow affected in stuttering. in fact, the available literature consistently suggests that not just speech breathing, but voluntary breathing in general, is aberrant in stuttering (5,12,19,33,34). Yet little is known of the prevalence of respiratory anomalies in stuttering, or of the role that such anomalies may play in this disorder. A major goal of the experiments proposed here is to test some basic aspects of respiratory sensation and motor control in stuttering as compared to normal subjects. Experiments are proposed to: 1) investigate stutterers' abilities to sense and to control respiratory-related pressures and lung volumes, compared to those of normal speakers; 2) describe in detail the respiratory discomfort (dyspnea) that often accompanies disfluency, and relate quality and intensity of dyspnea to breathing patterns; and 3) investigate the interactions of lung volume, linguistic structure, and voice onset time in stutterers' speech. Stuttering appears to be a heterogeneous disorder (2). A further goal of this proposal is to identify measures that can identify those stutterers in whom respiratory control contributes significantly to the disorder. Thus all methods are non-invasive, to enable the testing of relatively large numbers of subjects encompassing a broad range of severity levels. Identification of stuttering with a strong respiratory component is desirable as a first step toward designing clinical strategies that are designed to match the clients' needs. Also, a complete understanding of respiration in stuttering will almost certainly necessitate the use of some highly invasive techniques (e.g., recording diaphragmatic and laryngeal EMG). A knowledge of which subjects, and which aspects of respiration, are most compromised, would greatly improve the possibility of success in such investigations. Stuttering is not a rare disorder; the estimated prevalence in adults is approximately 1% of the population. Yet, a recent review of the attitudes of practicing speech-language pathologists revealed that stuttering in adults ranks among the disorders that practitioners are most uncomfortable in attempting to treat, in part because current therapies are inadequate (39). It is hoped that the work proposed here will help to improve this situation by contributing to current understanding of the role of voluntary respiratory control in stuttering.